Was looking around and it seems most people share the opinion that the black and white Wiis are identical when it comes to hardware. Any differences found would then be due to the laser reader for the disc being newer and less worn on the black Wiis.

So the best choice for me is to buy a white one because it has the build in hard drive which makes things easier and cheaper.

I honestly don't see any reason, why old disc-readers should be slower than new ones. But even if that is the case, it shows, that the difference is significant. If anyone buys a new Wii, he/she should definitely consider this, as you don't know, if you might run a Game, that is not on VC.